I'm just looking here and Dokan allows you to put a negative price on an item. Normally this isn't an issue if you run the entire store (why would you put a negative price!) however if you're allowing customers to post their own products they in theory could post a product for $-100 and then add $100 worth of products from other stores and then checkout with a $0 cart. Obviously an issue! I think Dokan should validate the price to ensure it's $0 or more (ie positive integer).